Travelling-wave tubes, klystrons and the like are electron tubes used for, e.g., amplification or oscillation of an RF signal by means of interaction between an electron beam emitted from an electron gun and a high-frequency circuit. Electron tube 1, for example, as illustrated in FIG. 1, includes electron gun 10 that emits electrons, helix 20 used as a circuit that makes electron beam 50 formed by the electrons emitted from electron gun 10 and an RF signal that interact with each other, collector electrode 30 that captures electrons output from helix 20, and anode electrode 40 that draws out electrons from electron gun 10 and guides the electrons emitted from electron gun 10 into a helical structure of helix 20. Electron gun 10 includes cathode electrode 11 that emits electrons (thermal electrons), heater 12 that provides cathode electrode 11 with thermal energy for electron emission, and wehnelt electrode 13 that makes electrons emitted from cathode electrode 11 converge to form electron beam 50.
Electrons emitted from electron gun 10, while forming electron beam 50, is accelerated by a difference in potential between cathode electrode 11 and anode electrode 40 and introduced into the helical structure of helix 20. The electrons travel inside the helical structure of helix 20 while interacting with an RF signal input from an end of helix 20. Electron beam 50 that has passed through the inside of the helical structure of helix 20 is captured by collector electrode 30. Here, the RF signal that has been amplified by the interaction with electron beam 50 is output from another end of helix 20.
Collector electrode 30 and electron gun 10 in electron tube 1 illustrated in FIG. 1 are each supplied with a predetermined power supply voltage from power supply apparatus 60. Anode electrode 40 and helix 20 are each connected to a case of electron tube 1 and grounded.
Cathode electrode 11 and wehnelt electrode 13 in electron gun 10 are each supplied with a common negative direct-current high voltage (helix voltage) from power supply apparatus 60, and heater 12 is supplied with the required direct-current or alternate-current voltage with reference to the potential of cathode electrode 11. Also, collector electrode 30 is supplied with a positive direct-current high voltage with reference to the potential of cathode electrode 11. Electron tube 1 may have a configuration in which anode electrode 40 and helix 20 are disconnected and anode electrode 40 is supplied with a positive direct-current voltage with reference to the potential of cathode electrode 11.
As illustrated in FIGS. 2A and 2B, helix 20 is supported and fixed by (normally, three) support rods 22 including a dielectric material, inside shell 21. Vanes 23 (also called “solids”) including a metal material are fixed to an inner wall of shell 21. The vanes 23 reduce variation in coupling impedance between an RF signal and electron beam 50 relative to frequency and also reduce variation in phase velocity of the RF signal to broaden a bandwidth of electron tube 1.
A technique that broadens the bandwidth of electron tube 1 by providing vanes inside a shell is also described in, for example, “Phase velocity dispersion of a solid metal segment loaded helix as used in broadband traveling wave tubes” (T. Onodera, Y. Tsuji, IEICE TRANSACTIONS on Electronics (Japanese edition), vol. J70-C, No. 9, pp. 1286-1287, September 1987). In the article, the shell is referred to as a “barrel” and the vanes are referred to as “metal segments.”
JP05-242817A describes a configuration in which one or both of the side surfaces of each of support rods (dielectric bodies) that support a helix is/are provided with a split-level portion and the split-level portion is plated with a metal to make the support rods function as vanes, thus eliminating the need for vanes.
Also, JP2006-134751A describes a configuration in which a conductive material is embedded in each of the support rods that support a helix to make the support rods function as vanes, thus eliminating the need for provide vanes.
For example, in a wireless communication system using electron tubes, an increase in the amount of data that can be transmitted/received per unit time can be expected by broadening the bandwidths of the electron tubes. Also, for example, in a radar system using electron tubes, the number of electron tubes covering a predetermined frequency range can be reduced by broadening the bandwidths of the electron tubes, thus enabling a reduction in, e.g., costs of the entire system and/or time required for maintenance.
Therefore, there is a demand for further broadening the bandwidths of electron tubes, and in order to respond to such demand, various studies have been underway. One of such studies relates to the aforementioned technique in which vanes including a metal material are provided inside a shell.
In recent years, there is a further increasing demand for broadening the bandwidths of electron tubes, and thus, it is desirable to provide an electron tube that can be used for a broader frequency band.